Display variable that user requests

I have a program that controls a robot and various systems that runs for hours or days on end. I want a way for the user to select a variable to display to screen through input. It would look something like this...

% Existing variables in code would look something like this
var1 = 10;
var2 = 3;
% The program asks user if they want to display a variable
x = input('Enter variable value to display: ','s')
%User inputs 'var2'
disp(x)
%Matlab displays the value of var2, which is 3

Right now, of course, it would display the string that was input, not the variable that the user selected with their string input. I feel like I want a function like str2var instead of str2num...

I could do a big switch statement for the most common variables that the user might want to select, but I was hoping there was a better way to do this. Ive tried searching the web, but couldn't come up with anything. Any advice would be very appreciated.

Answer 1

[Walter Roberson]

Perhaps just give them the Workspace Browser? https://www.mathworks.com/help/matlab/ref/workspace.html

You can find the names of all variables in the workspace using who or whos .

%set up for demo
aafdadf = 34213;
JO324adf = 3248.;
k_df9M = -121324;

varnames = setdiff( who(), 'varnames');

chosenvar = varnames{randi(numel(varnames))}

chosenvar = 'k_df9M'

H = str2func("@()evalin('caller', 'disp(" + chosenvar + ")');")

H = function_handle with value:
    @()evalin('caller','disp(k_df9M)')

H()

     -121324

[Kelsey]

Walter, thank you so much for your response. It certainly does what I want. I am not very familiar with using function handles, so while I was looking deeper into your response, I ran into the eval function, which I believe is exactly what I was looking for. I updated my code to be:

% Existing variables in code would look something like this
var1 = 10;
var2 = 3;
% The program asks user if they want to display a variable
x = input('Enter variable value to display: ','s');
%User inputs 'var2'
eval(sprintf('disp(%s)',x))
%Matlab displays the value of var2, which is 3

If the user can be trusted to not be mailicious, is there a reason why I couldn't use this simpler implementation? Or does your answer do additional things behind the scenes that I don't understand.

(As an aside, we can assume the user knows the name of the variable they want to display, so that isn't a problem. I will implement a check to make sure their selection is a valid variable name.)

[Walter Roberson]

If the user can be trusted to not be mailicious

A) They can't be trusted not to be malicious;

B) typing mistakes

Give them a menu to select from -- a drop-down box. And you can openvar() by name

x = 'var1';
openvar(x)

[Kelsey]

Thanks for your help with this!